Rho GTPases: Anti- or pro-neoplastic targets?

Exposure to BaA inhibits trophoblast cell invasion and induces miscarriage by regulating the DEC1/ARHGAP5 axis and promoting ubiquitination-mediated degradation of MMP2

Benz[a]anthracene (BaA), a hazardous polycyclic aromatic hydrocarbon classified by the EPA, is a probable reproductive toxicant. Epidemiological studies suggest that BaA exposure may be a risk factor for recurrent miscarriage (RM). However, the underlying mechanisms are not well understood. This study identified DEC1 as a key gene through RNA-seq and single-cell RNA sequencing analysis. DEC1 expression was found to be downregulated in villous tissues from women with RM and in primary extravillous trophoblasts (EVTs) exposed to BaA. BaA suppressed DEC1 expression by promoting abnormal methylation patterns. Further analysis revealed that ARHGAP5 is a direct target of DEC1 in EVTs, where DEC1 inhibits trophoblast invasion by directly regulating ARHGAP5 transcription. Additionally, BaA destabilized matrix metalloproteinase 2 (MMP2) by activating the aryl hydrocarbon receptor (AhR) and promoting E3 ubiquitin ligase MID1-mediated degradation. In a mouse model, BaA induced miscarriage by modulating the DEC1/ARHGAP5 and MID1/MMP2 axes. Notably, BaA-induced miscarriage in mice was prevented by DEC1 overexpression or MID1 knockdown. These findings indicate that BaA exposure leads to miscarriage by suppressing the DEC1/ARHGAP5 pathway and enhancing the MID1/MMP2 pathway in human EVTs.

Tumor-derived RHOA mutants interact with effectors in the GDP-bound state

RHOA mutations are found at diverse residues in various cancer types, implying mutation- and cell-specific mechanisms of tumorigenesis. Here, we focus on the underlying mechanisms of two gain-of-function RHOA mutations, A161P and A161V, identified in adult T-cell leukemia/lymphoma. We find that RHOAA161P and RHOAA161V are both fast-cycling mutants with increased guanine nucleotide dissociation/association rates compared with RHOAWT and show reduced GTP-hydrolysis activity. Crystal structures reveal an altered nucleotide association in RHOAA161P and an open nucleotide pocket in RHOAA161V. Both mutations perturb the dynamic properties of RHOA switch regions and shift the conformational landscape important for RHOA activity, as shown by 31P NMR and molecular dynamics simulations. Interestingly, RHOAA161P and RHOAA161V can interact with effectors in the GDP-bound state. 1H-15N HSQC NMR spectra support the existence of an active population in RHOAA161V-GDP. The distinct interaction mechanisms resulting from the mutations likely favor an RHOAWT-like "ON" conformation, endowing GDP-bound state effector binding activity.

FOXA2 Activates RND1 to Regulate Arachidonic Acid Metabolism Pathway and Suppress Cisplatin Resistance in Lung Squamous Cell Carcinoma

BACKGROUND

The primary cause of cancer-related fatalities globally is lung cancer. Although the chemotherapy drug cisplatin (DDP) has brought certain benefits to patients, the rapid development of drug resistance has greatly hindered treatment success.

METHODS

We used the lung squamous cell carcinoma (LUSC) mRNA data set to explore the differentially expressed gene (RND1) in LUSC and detected RND1 expression in LUSC cells and DDP-resistant cells by qRT-PCR. Meanwhile, we performed abnormal expression treatment on RND1 and conducted CCK8, colony formation, and flow cytometry to evaluate the impact of RND1 expression on cell proliferation, apoptosis, and DDP resistance. In addition, we analyzed metabolism pathways involving RND1 using GSEA. We also used online tools such as hTFtarget and JASPAR to screen for the upstream transcription factor FOXA2 of RND1 and verified their relationship through CHIP and dual luciferase experiments. Finally, we validated the role of FOXA2-RND1 in DDP resistance in LUSC through the above experiments.

RESULTS

RND1 was downregulated in LUSC, and overexpression of RND1 repressed proliferation and DDP resistance of LUSC cells and facilitated cell apoptosis. RND1 modulated the arachidonic acid (AA) metabolism pathway, and FOXA2 positively manipulated RND1 expression. By activating FOXA2, stabilizing RND1, and regulating AA levels, the sensitivity of LUSC cells to DDP could be enhanced.

CONCLUSION

Our study suggested that FOXA2 positively modulated the RND1-AA pathway, which repressed the resistance of LUSC cells to DDP.

Structural basis for the distinct roles of non-conserved Pro116 and conserved Tyr124 of BCH domain of yeast p50RhoGAP

p50RhoGAP is a key protein that interacts with and downregulates the small GTPase RhoA. p50RhoGAP is a multifunctional protein containing the BNIP-2 and Cdc42GAP Homology (BCH) domain that facilitates protein-protein interactions and lipid binding and the GAP domain that regulates active RhoA population. We recently solved the structure of the BCH domain from yeast p50RhoGAP (YBCH) and showed that it maintains the adjacent GAP domain in an auto-inhibited state through the β5 strand. Our previous WT YBCH structure shows that a unique kink at position 116 thought to be made by a proline residue between alpha helices α6 and α7 is essential for the formation of intertwined dimer from asymmetric monomers. Here we sought to establish the role and impact of this Pro116. However, the kink persists in the structure of P116A mutant YBCH domain, suggesting that the scaffold is not dictated by the proline residue at this position. We further identified Tyr124 (or Tyr188 in HBCH) as a conserved residue in the crucial β5 strand. Extending to the human ortholog, when substituted to acidic residues, Tyr188D or Tyr188E, we observed an increase in RhoA binding and self-dimerization, indicative of a loss of inhibition of the GAP domain by the BCH domain. These results point to distinct roles and impact of the non-conserved and conserved amino acid positions in regulating the structural and functional complexity of the BCH domain.

Circulating miRNAs and Preeclampsia: From Implantation to Epigenetics

In this review, we comprehensively present the literature on circulating microRNAs (miRNAs) associated with preeclampsia, a pregnancy-specific disease considered the primary reason for maternal and fetal mortality and morbidity. miRNAs are single-stranded non-coding RNAs, 20-24 nt long, which control mRNA expression. Changes in miRNA expression can induce a variation in the relative mRNA level and influence cellular homeostasis, and the strong presence of miRNAs in all body fluids has made them useful biomarkers of several diseases. Preeclampsia is a multifactorial disease, but the etiopathogenesis remains unclear. The functions of trophoblasts, including differentiation, proliferation, migration, invasion and apoptosis, are essential for a successful pregnancy. During the early stages of placental development, trophoblasts are strictly regulated by several molecular pathways; however, an imbalance in these molecular pathways can lead to severe placental lesions and pregnancy complications. We then discuss the role of miRNAs in trophoblast invasion and in the pathogenesis, diagnosis and prediction of preeclampsia. We also discuss the potential role of miRNAs from an epigenetic perspective with possible future therapeutic implications.

Recent advances in the development of Rho kinase inhibitors (2015-2021)

Rho-associated coiled-coil kinases (ROCKs) are key downstream effectors of small GTPases. ROCK plays a central role in diverse cellular events with accumulating evidence supporting the concept that ROCK is important in tumor development and progression. Numerous ROCK inhibitors have been investigated for their therapeutic potential in the treatment of cancers. In this article, we review recent research progress on ROCK inhibitors, especially those with potential for the treatment of cancers, reported in the literature from 2015 to 2021. Most ROCK inhibitors show potent in vitro and in vivo antitumor activities and have potential in the treatment of cancers.

ARHGEF16 expression correlates with proliferation, migration and invasion of colon cancer cells

Background

Rho guanine nucleotide exchange factor 16 (ARHGEF16) is a newly discovered Rho-family guanine nucleotide exchange factor (GEF) involved in the activation of Rho-family GTPases. However, its roles in colon cancer cell proliferation, migration, and invasion remain unknown. This study analyzed the expression of ARHGEF16 in colon cancer and explored its biological effects on colon cancer cells, so as to find new therapeutic targets for the treatment of colon cancer.

Methods

The expression of ARHGEF16 in colon cancer tissues and cells was detected by bioinformatics analysis, western blot, and quantitative real time polymerase chain reaction (qRT-PCR) assays. The effects of overexpression and silencing of ARHGEF16 on the biological behavior of colon cancer cells were examined by Cell Counting Kit-8 (CCK-8), cell scratching and Transwell assays.

Results

The database showed that ARHGEF16 was highly expressed in colon cancer tissues. Validation with clinical fresh tissue specimens and colon cancer cell lines revealed that ARHGEF16 was highly expressed in both. The proliferation, growth, migration, and invasion ability of colon cancer cell lines increased significantly with the overexpression of ARHGEF16, while silencing ARHGEF16 showed the opposite effect.

Conclusions

The expression of ARHGEF16 is closely related to the migration and invasive ability of colon cancer cells, and overexpression of ARHGEF16 promotes the migration and invasion of colon cancer cells and correlates with the metastatic potential of colon cancer.

Role of Rho GTPases in inflammatory bowel disease

Rat sarcoma virus homolog (Rho) guanosine triphosphatases (GTPases) function as "molecular switch" in cellular signaling regulation processes and are associated with the pathogenesis of inflammatory bowel disease (IBD). This chronic intestinal tract inflammation primarily encompasses two diseases: Crohn's disease and ulcerative colitis. The pathogenesis of IBD is complex and considered to include four main factors and their interactions: genetics, intestinal microbiota, immune system, and environment. Recently, several novel pathogenic components have been identified. In addition, potential therapies for IBD targeting Rho GTPases have emerged and proven to be clinically effective. This review mainly focuses on Rho GTPases and their possible mechanisms in IBD pathogenesis. The therapeutic possibility of Rho GTPases is also discussed.

RhoA G17E/Vav1 Signaling Induces Cancer Invasion via Matrix Metalloproteinase-9 in Gastric Cancer

BACKGROUND

RAS homolog family member A (RhoA), a member of the Rho family of small GTPases, and Vav1, a guanine nucleotide exchange factor for Rho family GTPases, have been reported to activate pathways related to the actin cytoskeleton and regulation of cell shape, attachment, and motility. The interaction between these molecules in lymphoma is involved in malignant signaling, but its function in epithelial malignancy is unknown. Here, we investigated the malignant signal of mutant RhoA in gastric cancer and demonstrated the potential of RhoA G17E/Vav1 as a therapeutic target for diffuse gastric cancer.

METHODS

The RhoA mutants R5W, G17E, and Y42C were retrovirally transduced into the gastric cancer cell line MKN74. The stably transduced cells were used for morphology, proliferation, and migration/invasion assays in vitro. MKN74 cells stably transduced with ectopic wild-type RhoA and mutant RhoA (G17E) were used in a peritoneal xenograft assay.

RESULTS

The RhoA mutations G17E and Y42C induced morphological changes in MKN74. G17E induced Vav1 expression at the mRNA and protein levels and promoted the migration and invasion of MKN74. An RNA interference assay of Vav1 revealed that RhoA G17E enhanced cancer cell invasion via Vav1. Furthermore, immunoprecipitation revealed that Vav1 and RhoA G17E specifically bind and function together through matrix metalloproteinase -9. In a peritoneal xenograft model of nude mice, RhoA G17E promoted peritoneal dissemination, whereas Vav1 knockdown suppressed it.

CONCLUSION

Overall, our findings indicate that RhoA G17E is associated with Vav1 and promoted cancer invasion via matrix metalloproteinase -9 in gastric cancer cells. Thus, RhoA G17E/Vav1 signaling in diffuse gastric cancer may be a useful therapeutic target.

The role of cyclins in the development and progression of prostate cancer

The role of cyclins in hormone-dependent neoplasms is crucial in the development of the disease that is resistant to first-line therapy, as the example of breast cancer shows. However, in prostate cancer, cyclins are studied to a lesser extent. There are some well-described molecular pathways, including cyclins A1 and D1 signaling, however the role of other cyclins, e.g., D2, D3, E, and H, still requires further investigation. Recent studies indicate that cyclins regulate various cellular processes, not only the cell cycle. Furthermore, they remain in cross-talk with many other signaling pathways, e.g., MAPK/ERK, PI3K/Akt, and Notch. The androgen signaling axis, which is pivotal in prostate cancer progression, interferes with cyclin pathways at many levels. This article summarizes current knowledge on the influence of cyclins on prostate cancer progression by describing interactions between the androgen receptor and cyclins, as well as mechanisms underlying the development of resistance to currently used therapies.

RHOA takes the RHOad less traveled to cancer

RAS and RHO GTPases function as signaling nodes that regulate diverse cellular processes. Whereas RAS mutations were identified in human cancers nearly four decades ago, only recently have mutations in two RHO GTPases, RAC1 and RHOA, been identified in cancer. RAS mutations are found in a diverse spectrum of human cancer types. By contrast, RAC1 and RHOA mutations are associated with distinct and restricted cancer types. Despite a conservation of RAS and RAC1 residues that comprise mutational hotspots, RHOA mutations comprise highly divergent hotspots. Whereas RAS and RAC1 act as oncogenes, RHOA may act as both an oncogene and a tumor suppressor. Thus, while RAS and RHO each take different mutational paths, they arrive at the same biological destination as cancer drivers.

Multi-omic profiling of peritoneal metastases in gastric cancer identifies molecular subtypes and therapeutic vulnerabilities

Peritoneal metastasis, a hallmark of incurable advanced gastric cancer (GC), presently has no curative therapy and its molecular features have not been examined extensively. Here we present a comprehensive multi-omic analysis of malignant ascitic fluid samples and their corresponding tumor cell lines from 98 patients, including whole-genome sequencing, RNA sequencing, DNA methylation and enhancer landscape. We identify a higher frequency of receptor tyrosine kinase and mitogen-activated protein kinase pathway alterations compared to primary GC; moreover, approximately half of the gene alterations are potentially treatable with targeted therapy. Our analyses also stratify ascites-disseminated GC into two distinct molecular subtypes: one displaying active super enhancers (SEs) at the ELF3, KLF5 and EHF loci, and a second subtype bearing transforming growth factor-β (TGF-β) pathway activation through SMAD3 SE activation and high expression of transcriptional enhancer factor TEF-1 (TEAD1). In the TGF-β subtype, inhibition of the TEAD pathway circumvents therapy resistance, suggesting a potential molecular-guided therapeutic strategy for this subtype of intractable GC.

Aberrant Expression and Subcellular Localization of ECT2 Drives Colorectal Cancer Progression and Growth

ECT2 is an activator of RHO GTPases that is essential for cytokinesis. In addition, ECT2 was identified as an oncoprotein when expressed ectopically in NIH/3T3 fibroblasts. However, oncogenic activation of ECT2 resulted from N-terminal truncation, and such truncated ECT2 proteins have not been found in patients with cancer. In this study, we observed elevated expression of full-length ECT2 protein in preneoplastic colon adenomas, driven by increased ECT2 mRNA abundance and associated with APC tumor-suppressor loss. Elevated ECT2 levels were detected in the cytoplasm and nucleus of colorectal cancer tissue, suggesting cytoplasmic mislocalization as one mechanism of early oncogenic ECT2 activation. Importantly, elevated nuclear ECT2 correlated with poorly differentiated tumors, and a low cytoplasmic:nuclear ratio of ECT2 protein correlated with poor patient survival, suggesting that nuclear and cytoplasmic ECT2 play distinct roles in colorectal cancer. Depletion of ECT2 reduced anchorage-independent cancer cell growth and invasion independent of its function in cytokinesis, and loss of Ect2 extended survival in a Kras G12D Apc-null colon cancer mouse model. Expression of ECT2 variants with impaired nuclear localization or guanine nucleotide exchange catalytic activity failed to restore cancer cell growth or invasion, indicating that active, nuclear ECT2 is required to support tumor progression. Nuclear ECT2 promoted ribosomal DNA transcription and ribosome biogenesis in colorectal cancer. These results support a driver role for both cytoplasmic and nuclear ECT2 overexpression in colorectal cancer and emphasize the critical role of precise subcellular localization in dictating ECT2 function in neoplastic cells. SIGNIFICANCE: ECT2 overexpression and mislocalization support its role as a driver in colon cancer that is independent from its function in normal cell cytokinesis.

The role of GTPase-activating protein ARHGAP26 in human cancers

Rho GTPases are molecular switches that play an important role in regulating the behavior of a variety of tumor cells. RhoA GTPase-activating protein 26 (ARHGAP26) is a GTPase-activating protein and inhibits the activity of Rho GTPases by promoting the hydrolytic ability of Rho GTPases. It also affects tumorigenesis and progression of various tumors through several methods, including formation of abnormal fusion genes and circular RNA. This review summarizes the biological functions and molecular mechanisms of ARHGAP26 in different tumors, proposes the potential clinical value of ARHGAP26 in cancer treatment, and discusses current issues that need to be addressed.

Structural basis for p50RhoGAP BCH domain-mediated regulation of Rho inactivation

Spatiotemporal regulation of signaling cascades is crucial for various biological pathways, under the control of a range of scaffolding proteins. The BNIP-2 and Cdc42GAP Homology (BCH) domain is a highly conserved module that targets small GTPases and their regulators. Proteins bearing BCH domains are key for driving cell elongation, retraction, membrane protrusion, and other aspects of active morphogenesis during cell migration, myoblast differentiation, and neuritogenesis. We previously showed that the BCH domain of p50RhoGAP (ARHGAP1) sequesters RhoA from inactivation by its adjacent GAP domain; however, the underlying molecular mechanism for RhoA inactivation by p50RhoGAP remains unknown. Here, we report the crystal structure of the BCH domain of p50RhoGAP Schizosaccharomyces pombe and model the human p50RhoGAP BCH domain to understand its regulatory function using in vitro and cell line studies. We show that the BCH domain adopts an intertwined dimeric structure with asymmetric monomers and harbors a unique RhoA-binding loop and a lipid-binding pocket that anchors prenylated RhoA. Interestingly, the β5-strand of the BCH domain is involved in an intermolecular β-sheet, which is crucial for inhibition of the adjacent GAP domain. A destabilizing mutation in the β5-strand triggers the release of the GAP domain from autoinhibition. This renders p50RhoGAP active, thereby leading to RhoA inactivation and increased self-association of p50RhoGAP molecules via their BCH domains. Our results offer key insight into the concerted spatiotemporal regulation of Rho activity by BCH domain-containing proteins.

NDRG1 regulates Filopodia-induced Colorectal Cancer invasiveness via modulating CDC42 activity

N-myc downstream regulated gene-1 (NDRG1) has been identified as a putative metastasis suppressor gene and proved to be a key player in cancer spreading and proliferation in our previous work. However, the effects of NDRG1 on tumor invasion and the mechanisms behind it are rarely understood. Here we provided in silico evidence that NDRG1 plays a crucial role in actin reorganization in colorectal cancer (CRC). Through in vitro experiments, we next observed filopodia formation was altered in NDRG1-modified cell lines, while cell division cycle-42 (CDC42) displayed excessive activation in NDRG1-silenced cells. Mechanistically, NDRG1 loss disrupts the binding between RhoGDIα and CDC42 and triggers the activation of CDC42 and the downstream cascades PAK1/Cofilin, thereby promotes the formation of filopodia and invasiveness of CRC. The knockdown of NDRG1 led to enhanced dissemination of CRC cells in vivo and correlates with active CDC42 expression. Using clinical sample analysis, we found an elevated level of active CDC42 in patients with advanced T stage, and it was negatively related to NDRG1 expression. In sum, these results uncover a mechanism utilized by NDRG1 to regulate CDC42 activity in coordinating cytoskeleton reorganization, which was crucial in cancer invasion.

Nanobody-Based Quantification of GTP-Bound RHO Conformation Reveals RHOA and RHOC Activation Independent from Their Total Expression in Breast Cancer

As key regulators of the actin cytoskeleton, RHO GTPase expression and/or activity are deregulated in tumorigenesis and metastatic progression. Nevertheless, the vast majority of experiments supporting this conclusion was conducted on cell lines but not on human tumor samples that were mostly studied at the expression level only. Up to now, the activity of RHO proteins remains poorly investigated in human tumors. In this article, we present the development of a robust nanobody-based ELISA assay, with a high selectivity that allows an accurate quantification of RHO protein GTP-bound state in the nanomolar range (1 nM; 20 μg/L), not only in cell lines after treatment but also in tumor samples. Of note, we present here a fine analysis of RHOA-like and RAC1 active state in tumor samples with the most comprehensive study of RHOA-GTP and RHOC-GTP levels performed on human breast tumor samples. We revealed increased GTP-bound RHOA and RHOC protein activities in tumors compared to normal tissue counterparts, and demonstrated that the RHO active state and RHO expression are two independent parameters among different breast cancer subtypes. Our results further highlight the regulation of RHO protein activation in tumor samples and the relevance of directly studying RHO GTPase activities involvement in molecular pathways.

Group I p21-activated kinases in leukemia cell adhesion to fibronectin

P21-activated kinases (PAK) regulate processes associated with cytoskeleton dynamics. PAK expression in leukemia cells was measured on protein and mRNA levels. In functional assays, we analyzed the effect of PAK inhibitors IPA-3 and FRAX597 on cell adhesivity and viability. PAK2 was dominant in cell lines, whereas primary cells also expressed comparable amount of PAK1 transcription isoforms: PAK1-full and PAK1Δ15. PAK1Δ15 and PAK2 levels correlated with surface density of integrins β1 and αVβ3. PAK1-full, but not PAK2, was present in membrane protrusions. IPA-3, which prevents PAK activation, induced cell contraction in semi-adherent HEL cells only. FRAX597, which inhibits PAK kinase activity, increased cell-surface contact area in all leukemia cells. Both inhibitors reduced the stability of cell attachment and induced cell death.

The R-enantiomer of ketorolac reduces ovarian cancer tumor burden in vivo

BACKGROUND

Rho-family GTPases, including Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42), are important modulators of cancer-relevant cell functions and are viewed as promising therapeutic targets. Based on high-throughput screening and cheminformatics we identified the R-enantiomer of an FDA-approved drug (ketorolac) as an inhibitor of Rac1 and Cdc42. The corresponding S-enantiomer is a non-steroidal anti-inflammatory drug (NSAID) with selective activity against cyclooxygenases. We reported previously that R-ketorolac, but not the S-enantiomer, inhibited Rac1 and Cdc42-dependent downstream signaling, growth factor stimulated actin cytoskeleton rearrangements, cell adhesion, migration and invasion in ovarian cancer cell lines and patient-derived tumor cells.

METHODS

In this study we treated mice with R-ketorolac and measured engraftment of tumor cells to the omentum, tumor burden, and target GTPase activity. In order to gain insights into the actions of R-ketorolac, we also performed global RNA-sequencing (RNA-seq) analysis on tumor samples.

RESULTS

Treatment of mice with R-ketorolac decreased omental engraftment of ovarian tumor cells at 18 h post tumor cell injection and tumor burden after 2 weeks of tumor growth. R-ketorolac treatment inhibited tumor Rac1 and Cdc42 activity with little impact on mRNA or protein expression of these GTPase targets. RNA-seq analysis revealed that R-ketorolac decreased expression of genes in the HIF-1 signaling pathway. R-ketorolac treatment also reduced expression of additional genes associated with poor prognosis in ovarian cancer.

CONCLUSION

These findings suggest that R-ketorolac may represent a novel therapeutic approach for ovarian cancer based on its pharmacologic activity as a Rac1 and Cdc42 inhibitor. R-ketorolac modulates relevant pathways and genes associated with disease progression and worse outcome.

Recombinant anthrax lethal toxin inhibits cell motility and invasion in breast cancer cells through the dysregulation of Rho GTPases

Breast cancer is the leading cause of cancer-associated death among women worldwide. Targeting breast cancer cell metastasis is an important therapeutic approach. The MAPK pathway is a key cell signaling pathway that plays a pivotal role in cellular invasion and migration. Numerous studies have identified the MAPK pathway as a way to target cell survival and motility. The present study treated MBA-MD-231 breast cancer cells with anthrax lethal toxin (LeTx), a potent MAPK inhibitor that selectively cleaves and inactivates all MEKs, as a potential therapeutic method to inhibit breast cancer cell migration. LeTx has been demonstrated to affect breast cancer cell migration. Cells treated with LeTx showed a significant decrease in motility, as observed using wound healing and random 2D motility assays. Additionally, cells treated with LeTx showed an increase in adhesion, which would explain the decrease in migration. Pull-down assays examining the activation status of the members of the Rho family of GTPases revealed an increase in RhoA activation accompanied by a decrease in Cdc42 activation following LeTx treatment. Finally, LeTx mediated a decrease in invasion using a Boyden chamber assay, which could be a result of the decrease in Cdc42 activation. The present study reported the effect of LeTx treatment on the migration, adhesion and invasion of breast cancer cells, demonstrating that this effect was associated with the dysregulation of the Rho GTPases, RhoA and Cdc42.

Rhoj Is a Novel Target for Progression and Invasion of Glioblastoma by Impairing Cytoskeleton Dynamics

Rho GTPase family members were identified as critical regulators of cell morphology, actin cytoskeleton organization, cell movement, and cell cycle and also contributed to tumor progression, which have been implicated in various types of cancer metastasis and growth. Here, we firstly reported the dysregulation of Rhoj in glioblastoma multiforme (GBM) and aimed to investigate the role and mechanism of Rhoj in GBM. We analyzed the expression of 21 Rho GTPases family members and validated the expression of Rhoj in GBM by immunohistochemistry. We further investigated the role and mechanism of Rhoj in GBM both in vitro and in vivo. We observed that Rhoj is significantly overexpressed in GBM and associated with patients' survival. However, the role and underlying molecular mechanism of Rhoj in GBM are still unclear. We demonstrated that transcription factor c-Jun regulated the expression of Rhoj, and Rhoj interacted with moesin to promote GBM cell proliferation and migration by potentiating the activation of Rac1/PAK pathway and cytoskeletal dynamics. Rhoj may promote migration and invasion of GBM cells by regulating epithelial-mesenchymal transition (EMT)-like process. In conclusion, the Rhoj/Rac1/PAK signaling mediates invasion and progression of GBM and is a potential therapeutic target for GBM treatment. Rhoj may also be a promising biomarker for GBM diagnosis and prognosis.

Examination of clinically-derived p210 BCR/ABL1 RhoGEF mutations in a murine bone marrow transplantation model of CML

Expression of the p210 BCR/ABL1 fusion protein has been described in virtually all patients with chronic myelogenous leukemia (CML). Previous studies have identified a guanine nucleotide exchange factor (RhoGEF) domain within BCR that is retained in p210 BCR/ABL1. Missense mutations at residues T654 (T654K) and F547 (F547L) within this domain have been reported in a CML patient in blast crisis (BC). In this study, we have evaluated p210 BCR/ABL1 constructs that contain these substitutions in a murine bone marrow transplantation (BMT) model of CML. The mutants exhibit normal expression and tyrosine kinase activity but altered signaling. When examined in the BMT assay, mice that express the mutants exhibit earlier onset of disease but have significantly extended lifespans relative to mice that express unmodified p210 BCR/ABL1. While mice that express p210 BCR/ABL1 exhibit neutrophilia that progresses to a less differentiated phenotype at death, disease in the mutant mice is characterized by eosinophilia with no maturation arrest. This observation was confirmed in vitro using myeloid cells and was associated with enhanced p53 phosphorylation and G1/S arrest. These results suggest that residues within the RhoGEF domain of p210 BCR/ABL1 can influence disease progression.

FYN is required for ARHGEF16 to promote proliferation and migration in colon cancer cells

ARHGEF16 is a recently identified Rho-family guanine nucleotide exchange factor (GEF) that has been implicated in the activation of Rho-family GTPases such as Rho G, Rac, and Cdc42. However, its functions in colon cancer cell proliferation and migration are not well understood. In this study, we showed that ARHGEF16 was highly expressed in clinical specimens of colon cancer. In colon cancer cells, ARHGEF16-stimulated proliferation and migration in vitro and in vivo. Furthermore, we identified a nonreceptor tyrosine kinase, FYN, as a novel partner of ARHGEF16. Knocking down FYN expression decreased ARHGEF16 protein level in colon cancer cells. We further demonstrated that ARHGEF16-induced colon cancer cell proliferation and migration were dependent on FYN since knockdown FYN abolished the ARHGEF16-induced proliferation and migration of colon cancer cells. The FYN-ARHGEF16 axis mediates colon cancer progression and is a potential therapeutic target for colon cancer treatment.

Hormones Secretion and Rho GTPases in Neuroendocrine Tumors

Neuroendocrine tumors (NETs) belong to a heterogeneous group of neoplasms arising from hormone secreting cells. These tumors are often associated with a dysfunction of their secretory activity. Neuroendocrine secretion occurs through calcium-regulated exocytosis, a process that is tightly controlled by Rho GTPases family members. In this review, we compiled the numerous mutations and modification of expression levels of Rho GTPases or their regulators (Rho guanine nucleotide-exchange factors and Rho GTPase-activating proteins) that have been identified in NETs. We discussed how they might regulate neuroendocrine secretion.

A New Rho(d) Map to Diffuse Gastric Cancer

Diffuse gastric cancer (DGC) is characterized by frequent missense mutations in the small GTPase RHOA, but the effects of this mutation on enzyme activity and signaling have been widely debated. In this issue, Zhang and colleagues show that the most common RHOA mutation in DGC, encoding RHOA^Y42C, represents a gain of function; that a mouse model incorporating this mutation in association with loss of the E-cadherin gene CDH1 recapitulates many aspects of DGC; and that rationally designed therapeutics based on our understanding of RHOA signaling are promising agents for treating DGC.See related article by Zhang et al., p. 288.

Vav2 pharmaco-mimetic mice reveal the therapeutic value and caveats of the catalytic inactivation of a Rho exchange factor

The current paradigm holds that the inhibition of Rho guanosine nucleotide exchange factors (GEFs), the enzymes that stimulate Rho GTPases, can be a valuable therapeutic strategy to treat Rho-dependent tumors. However, formal validation of this idea using in vivo models is still missing. In this context, it is worth remembering that many Rho GEFs can mediate both catalysis-dependent and independent responses, thus raising the possibility that the inhibition of their catalytic activities might not be sufficient per se to block tumorigenic processes. On the other hand, the inhibition of these enzymes can trigger collateral side effects that could preclude the practical implementation of anti-GEF therapies. To address those issues, we have generated mouse models to mimic the effect of the systemic application of an inhibitor for the catalytic activity of the Rho GEF Vav2 at the organismal level. Our results indicate that lowering the catalytic activity of Vav2 below specific thresholds is sufficient to block skin tumor initiation, promotion, and progression. They also reveal that the negative side effects typically induced by the loss of Vav2 can be bypassed depending on the overall level of Vav2 inhibition achieved in vivo. These data underscore the pros and cons of anti-Rho GEF therapies for cancer treatment. They also support the idea that Vav2 could represent a viable drug target.

Rho GTPases in Gynecologic Cancers: In-Depth Analysis toward the Paradigm Change from Reactive to Predictive, Preventive, and Personalized Medical Approach Benefiting the Patient and Healthcare

Rho guanosine triphospatases (GTPases) resemble a conserved family of GTP-binding proteins regulating actin cytoskeleton dynamics and several signaling pathways central for the cell. Rho GTPases create a so-called Ras-superfamily of GTPases subdivided into subgroups comprising at least 20 members. Rho GTPases play a key regulatory role in gene expression, cell cycle control and proliferation, epithelial cell polarity, cell migration, survival, and apoptosis, among others. They also have tissue-related functions including angiogenesis being involved in inflammatory and wound healing processes. Contextually, any abnormality in the Rho GTPase function may result in severe consequences at molecular, cellular, and tissue levels. Rho GTPases also play a key role in tumorigenesis and metastatic disease. Corresponding mechanisms include a number of targets such as kinases and scaffold/adaptor-like proteins initiating GTPases-related signaling cascades. The accumulated evidence demonstrates the oncogenic relevance of Rho GTPases for several solid malignancies including breast, liver, bladder, melanoma, testicular, lung, central nervous system (CNS), head and neck, cervical, and ovarian cancers. Furthermore, Rho GTPases play a crucial role in the development of radio- and chemoresistance e.g. under cisplatin-based cancer treatment. This article provides an in-depth overview on the role of Rho GTPases in gynecological cancers, highlights relevant signaling pathways and pathomechanisms, and sheds light on their involvement in tumor progression, metastatic spread, and radio/chemo resistance. In addition, insights into a spectrum of novel biomarkers and innovative approaches based on the paradigm shift from reactive to predictive, preventive, and personalized medicine are provided.

Investigation of the role and mechanism of ARHGAP5-mediated colorectal cancer metastasis

Background: Metastatic colorectal cancer (CRC) is a lethal disease; however, the underlying molecular mechanisms remain unclear and require further study. Methods: RNA-Seq, PCR, Western blotting, immunohistochemistry, ChIP and RNAi assays were performed to investigate Rho GTPase-activating protein 5 (ARHGAP5, aslo known as p190RhoGAP-B, p190-B) expression and the clinical relevance, functional roles and regulatory mechanisms of this protein using human CRC cells and tissues. In vivo, two cell-based xenograft models were used to evaluate the roles of ARHGAP5 in CRC metastasis. Results: Here, we report that ARHGAP5 expression is significantly increased in metastatic CRC tissues and is inversely associated with patient overall survival. The suppression of ARHGAP5 reduces CRC cell metastasis in vitro and in cell-based xenograft models. Furthermore, we show that ARHGAP5 promotes CRC cell epithelial-mesenchymal transition by negatively regulating RhoA activity. Mechanistically, cAMP response element-binding protein (CREB1) transcriptionally upregulates ARHGAP5 expression, and decreased miR-137 further contributes to ARHGAP5 mRNA stability in CRC. Conclusions: Overall, our study highlights the crucial function of ARHGAP5 in CRC metastasis, thus suggesting novel prognostic biomarkers and hypothetical therapeutic targets.

PAK1, PAK1Δ15, and PAK2: similarities, differences and mutual interactions

P21-activated kinases (PAK) are key effectors of the small GTPases Rac1 and Cdc42, as well as of Src family kinases. In particular, PAK1 has several well-documented roles, both kinase-dependent and kinase-independent, in cancer-related processes, such as cell proliferation, adhesion, and migration. However, PAK1 properties and functions have not been attributed to individual PAK1 isoforms: besides the full-length kinase (PAK1-full), a splicing variant lacking the exon 15 (PAK1Δ15) is annotated in protein databases. In addition, it is not clear if PAK1 and PAK2 are functionally overlapping. Using fluorescently tagged forms of human PAK1-full, PAK1Δ15, and PAK2, we analyzed their intracellular localization and mutual interactions. Effects of PAK inhibition (IPA-3, FRAX597) or depletion (siRNA) on cell-surface adhesion were monitored by real-time microimpedance measurement. Both PAK1Δ15 and PAK2, but not PAK1-full, were enriched in focal adhesions, indicating that the C-terminus might be important for PAK intracellular localization. Using coimmunoprecipitation, we documented direct interactions among the studied PAK group I members: PAK1 and PAK2 form homodimers, but all possible heterocomplexes were also detected. Interaction of PAK1Δ15 or PAK2 with PAK1-full was associated with extensive PAK1Δ15/PAK2 cleavage. The impedance measurements indicate, that PAK2 depletion slows down cell attachment to a surface, and that PAK1-full is involved in cell spreading. Altogether, our data suggest a complex interplay among different PAK group I members, which have non-redundant functions.

Reduced RhoA expression enhances breast cancer metastasis with a concomitant increase in CCR5 and CXCR4 chemokines signaling

The role of RhoA GTPases in breast cancer tumorigenesis and metastasis is unclear. Early studies within which mutations in RhoA were designed based on cancer-associated mutations in Ras supported an oncogene role for RhoA. However, recent whole-genome sequencing studies of cancers raised the possibility that RhoA may have a tumor suppression function. Here, using a syngeneic triple negative breast cancer murine model we investigated the physiological effects of reduced RhoA expression on breast cancer tumorigenesis and metastasis. RhoA knockdown had no effect on primary tumor formation and tumor proliferation, concurring with our in vitro findings where reduced RhoA had no effect on breast cancer cell proliferation and clonogenic growth. In contrast, primary tumors with RhoA knockdown efficiently invaded sentinel lymph nodes and significantly metastasized to lungs compared to control tumors. Mechanistically, the current study demonstrated that this is achieved by promoting a pro-tumor microenvironment, with increased cancer-associated fibroblasts and macrophage infiltration, and by modulating the CCL5-CCR5 and CXCL12-CXCR4 chemokine axes in the primary tumor. To our knowledge, this is the first such mechanistic study in breast cancer showing the ability of RhoA to suppress chemokine receptor expression in breast tumor cells. Our work suggests a physiological lung and lymph node metastasis suppressor role for RhoA GTPase in breast cancer.

A Targeted Protein Degradation Cell-Based Screening for Nanobodies Selective toward the Cellular RHOB GTP-Bound Conformation

The selective downregulation of activated intracellular proteins is a key challenge in cell biology. RHO small GTPases switch between a guanosine diphosphate (GDP)-bound and a guanosine triphosphate (GTP)-bound state that drives downstream signaling. At present, no tool is available to study endogenous RHO-GTPinduced conformational changes in live cells. Here, we established a cell-based screen to selectively degrade RHOB-GTP using F-box-intracellular single-domain antibody fusion. We identified one intracellular antibody (intrabody) that shows selective targeting of endogenous RHOB-GTP mediated by interactions between the CDR3 loop of the domain antibody and the GTP-binding pocket of RHOB. Our results suggest that, while RHOB is highly regulated at the expression level, only the GTP-bound pool, but not its global expression, mediates RHOB functions in genomic instability and in cell invasion. The F-box/intrabody-targeted protein degradation represents a unique approach to knock down the active form of small GTPases or other proteins with multiple cellular activities.

Rho GTPases in cancer: friend or foe?

The Rho GTPases RhoA, Rac1, and Cdc42 are important regulators of cytoskeletal dynamics. Although many in vitro and in vivo data indicate tumor-promoting effects of activated Rho GTPases, also tumor suppressive functions have been described, suggesting either highly cell-type-specific functions for Rho GTPases in cancer or insufficient cancer models. The availability of a large number of cancer genome-sequencing data by The Cancer Genome Atlas (TCGA) allows for the investigation of Rho GTPase function in human cancers in silico. This information should be used to improve our in vitro and in vivo cancer models, which are essential for a molecular understanding of Rho GTPase function in malignant tumors and for the potential development of cancer drugs targeting Rho GTPase signaling.

Dual Actions of Ketorolac in Metastatic Ovarian Cancer

Cytoreductive surgery and chemotherapy are cornerstones of ovarian cancer treatment, yet disease recurrence remains a significant clinical issue. Surgery can release cancer cells into the circulation, suppress anti-tumor immunity, and induce inflammatory responses that support the growth of residual disease. Intervention within the peri-operative window is an under-explored opportunity to mitigate these consequences of surgery and influence the course of metastatic disease to improve patient outcomes. One drug associated with improved survival in cancer patients is ketorolac. Ketorolac is a chiral molecule administered as a 1:1 racemic mixture of the S- and R-enantiomers. The S-enantiomer is considered the active component for its FDA indication in pain management with selective activity against cyclooxygenase (COX) enzymes. The R-enantiomer has a previously unrecognized activity as an inhibitor of Rac1 (Ras-related C3 botulinum toxin substrate) and Cdc42 (cell division control protein 42) GTPases. Therefore, ketorolac differs from other non-steroidal anti-inflammatory drugs (NSAIDs) by functioning as two distinct pharmacologic entities due to the independent actions of each enantiomer. In this review, we summarize evidence supporting the benefits of ketorolac administration for ovarian cancer patients. We also discuss how simultaneous inhibition of these two distinct classes of targets, COX enzymes and Rac1/Cdc42, by S-ketorolac and R-ketorolac respectively, could each contribute to anti-cancer activity.

The RND1 Small GTPase: Main Functions and Emerging Role in Oncogenesis

The Rho GTPase family can be classified into classic and atypical members. Classic members cycle between an inactive Guanosine DiPhosphate -bound state and an active Guanosine TriPhosphate-bound state. Atypical Rho GTPases, such as RND1, are predominantly in an active GTP-bound conformation. The role of classic members in oncogenesis has been the subject of numerous studies, while that of atypical members has been less explored. Besides the roles of RND1 in healthy tissues, recent data suggest that RND1 is involved in oncogenesis and response to cancer therapeutics. Here, we present the current knowledge on RND1 expression, subcellular localization, and functions in healthy tissues. Then, we review data showing that RND1 expression is dysregulated in tumors, the molecular mechanisms involved in this deregulation, and the role of RND1 in oncogenesis. For several aggressive tumors, RND1 presents the features of a tumor suppressor gene. In these tumors, low expression of RND1 is associated with a bad prognosis for the patients. Finally, we highlight that RND1 expression is induced by anticancer agents and modulates their response. Of note, RND1 mRNA levels in tumors could be used as a predictive marker of both patient prognosis and response to anticancer agents.

Targeted Quantitative Proteomics Revealed Arsenite-induced Proteasomal Degradation of RhoB in Fibroblast Cells

Arsenic is a toxicant widely present in the environment. Previous epidemiological and animal studies support that arsenic exposure is associated with elevated incidences of lung and skin cancers. Therefore, it is important to understand the molecular mechanisms through which arsenite initiates malignant transformation of lung and skin tissues. Ras superfamily of small GTPases assumes a crucial role in many cellular processes including transcription, protein synthesis, and trafficking. In addition, small GTPase signaling is known to be altered in many types of cancer. By employing a multiple-reaction monitoring (MRM)-based targeted proteomic method, we found that the protein level of RhoB was substantially decreased in IMR90 human lung fibroblast cells upon a 12-h exposure to 5 μM NaAsO2. In addition, the protein level of ectopically expressed RhoB was found to decline in a dose-dependent manner upon arsenite exposure in HEK293T, HeLa, and GM00637 cells as well as that of endogenous RhoB protein in IMR90 cells. Moreover, the arsenite-elicited down-regulation of RhoB was found to arise from enhanced proteasomal degradation. Taken together, we demonstrated, for the first time, that exposure to arsenite could attenuate the protein expression of RhoB through proteasomal degradation.

RHO Family GTPases in the Biology of Lymphoma

RHO GTPases are a class of small molecules involved in the regulation of several cellular processes that belong to the RAS GTPase superfamily. The RHO family of GTPases includes several members that are further divided into two different groups: typical and atypical. Both typical and atypical RHO GTPases are critical transducers of intracellular signaling and have been linked to human cancer. Significantly, both gain-of-function and loss-of-function mutations have been described in human tumors with contradicting roles depending on the cell context. The RAS family of GTPases that also belong to the RAS GTPase superfamily like the RHO GTPases, includes arguably the most frequently mutated genes in human cancers (K-RAS, N-RAS, and H-RAS) but has been extensively described elsewhere. This review focuses on the role of RHO family GTPases in human lymphoma initiation and progression.

Doxorubicin Promotes Migration and Invasion of Breast Cancer Cells through the Upregulation of the RhoA/MLC Pathway

Purpose

Cancer cells develop acquired resistance induced by chemotherapeutic drugs. In this study, we investigated the effects of brief treatment with cytotoxic drugs on the phenotype of breast cancer cells.

Methods

Breast cancer cells MCF7 and BT-474 were briefly treated with paclitaxel or doxorubicin. Clonogenic, migration, and invasion assays were performed on the treated cells. Western blot analysis and RhoA activity assay were also performed.

Results

Breast cancer cells when briefly treated with paclitaxel or doxorubicin showed reduced clonogenic ability. Doxorubicin, but not paclitaxel, augmented cell migration and invasion. The invasion-promoting effects of doxorubicin were lost when the two drugs were sequentially used in combination. Myosin light chain (MLC) 2 phosphorylation and RhoA activity were upregulated by doxorubicin and downregulated by paclitaxel. Pretreatment with RhoA inhibitors abolished the migration- and invasion-promoting effects of doxorubicin.

Conclusion

Doxorubicin activates the RhoA/MLC pathway and enhances breast cancer cell migration and invasion. Therefore, this pathway might be explored as a therapeutic target to suppress anthracycline-enhanced tumor progression.

Isoprenylcysteine carboxy methyltransferase (ICMT) is associated with tumor aggressiveness and its expression is controlled by the p53 tumor suppressor

Isoprenyl cysteine carboxyl methyltransferase (ICMT) plays a key role in post-translational regulation of prenylated proteins. On the basis of previous results, we hypothesized that the p53 pathway and ICMT expression may be linked in cancer cells. Here, we studied whether WT p53 and cancer-associated p53 point mutants regulate ICMT levels and whether ICMT overexpression affects tumor progression. Studying the effect of p53 variants on ICMT mRNA and protein levels in cancer cells, we found that WT p53 and p53 mutants differentially affect ICMT expression, indicating that p53 status influences ICMT levels in tumors. To investigate the underlying mechanisms, we constructed ICMT-luciferase reporters and found that WT p53 represses ICMT transcription. In contrast, p53 mutants showed a positive effect on ICMT expression. Promoter truncation analyses pinpointed the repressive effect of WT p53 to the -209 and -14 region on the ICMT promoter, and ChIP assays indicated that WT p53 is recruited to this region. Instead, a different promoter region was identified as responsible for the mutant p53 effect. Studying the effect of ICMT overexpression on tumor-associated phenotypes in vitro and in vivo, and analyzing breast and lung cancer databases, we identified a correlation between p53 status and ICMT expression in breast and lung cancers. Moreover, we observed that ICMT overexpression is correlated with negative clinical outcomes. Our work unveils a link between postprenylation protein processing and the p53 pathway, indicating that the functional interplay between WT and mutant p53 alters ICMT levels, thereby affecting tumor aggressiveness.

Selection and Characterization of a Nanobody Biosensor of GTP-Bound RHO Activities

RHO (Ras HOmologous) GTPases are molecular switches that activate, in their state bound to Guanosine triphosphate (GTP), key signaling pathways, which involve actin cytoskeleton dynamics. Previously, we selected the nanobody RH12, from a synthetic phage display library, which binds the GTP-bound active conformation of RHOA (Ras Homologous family member A). However, when expressed as an intracellular antibody, its blocking effect on RHO signaling led to a loss of actin fibers, which in turn affected cell shape and cell survival. Here, in order to engineer an intracellular biosensor of RHOA-GTP activation, we screened the same phage nanobody library and identified another RHO-GTP selective intracellular nanobody, but with no apparent toxicity. The recombinant RH57 nanobody displays high affinity towards GTP-bound RHOA/B/C subgroup of small GTPases in vitro. Intracellular expression of the RH57 allowed selective co-precipitation with the GTP-bound state of the endogenous RHOA subfamily. When expressed as a fluorescent fusion protein, the chromobody GFP-RH57 was localized to the inner plasma membrane upon stimulation of the activation of endogenous RHO. Finally, the RH57 nanobody was used to establish a BRET-based biosensor (Bioluminescence Resonance Energy Transfer) of RHO activation. The dynamic range of the BRET signal could potentially offer new opportunities to develop cell-based screening of RHOA subfamily activation modulators.

Rho GTPase Activating Protein 24 (ARHGAP24) Regulates the Anti-Cancer Activity of Sorafenib Against Breast Cancer MDA-MB-231 Cells via the Signal Transducer and Activator of Transcription 3 (STAT3) Signaling Pathway

BACKGROUND STAT3 has emerged as a novel potential target for sorafenib, a multikinase inhibitor, in the context of cancer therapy. ARHGAP24 is a Rac-specific Rho GTPase-activating protein (Rho GAP), which can convert Rho GTPases to an inactive state. It has been proved to be an oncosuppressor protein in renal cancer. In the present study, we investigated its anti-cancer effect in breast cancer (BC). MATERIAL AND METHODS Quantitative real-time PCR (qRT-PCR) and Western blot analysis were performed to detect the expression of ARHGAP24 in clinical tissue samples. Then, BC MDA-MB-231 cells were virally transduced with ARHGAP24 silencing or overexpression lentiviral vectors in the absence or presence of sorafenib. Cell viability and metastatic ability were evaluated by using the Cell Counting Kit-8 (CCK-8) and Transwell assays. Proteins belonging to the STAT3 pathway were detected by Western blot. RESULTS ARHGAP24 decreased in BC tissues compared with the adjacent normal tissues. Forced expression of ARHGAP24 and sorafenib treatment significantly suppressed the viability, migration, and invasion of MDA-MB-231 cells. Conversely, elimination of the endogenous ARHGAP24 with shRNA promoted cell viability, migration, and invasion. The phosphorylation of STAT3 and the expression of MMP-2 and MMP-9 were attenuated by ARHGAP24 ectopic expression and sorafenib treatment. Furthermore, forced expression of ARHGAP24 significantly enhanced sorafenib-induced decrease of cell viability, migration, and invasion of MDA-MB-231 cells, while elimination of the endogenous ARHGAP24 with shRNA inhibited it. CONCLUSIONS ARHGAP24 can suppress the development of MDA-MB-231 cells via the STAT3 signaling pathway, and sorafenib inhibits cell viability, migration, invasion, and STAT3 activation in MDA-MB-231 cells through ARHGAP24.

Statins: a new approach to combat temozolomide chemoresistance in glioblastoma

Patients with glioblastoma multiforme (GBM) have an average life expectancy of approximately 15 months. Recently, statins have emerged as a potential adjuvant cancer therapy due to their ability to inhibit cell proliferation and induce apoptosis in many types of cancer. The exact mechanisms that mediate the inhibitory actions of statins in cancer cells are largely unknown. The purpose of this proceeding paper is to discuss some of the known anticancer effects of statins, while focusing on GBM therapy that includes adjunct therapy of statins with chemotherapeutic agents.

Studying how genetic variants affect mechanism in biological systems

Genetic variants are currently a major component of system-wide investigations into biological function or disease. Approaches to select variants (often out of thousands of candidates) that are responsible for a particular phenomenon have many clinical applications and can help illuminate differences between individuals. Selecting meaningful variants is greatly aided by integration with information about molecular mechanism, whether known from protein structures or interactions or biological pathways. In this review we discuss the nature of genetic variants, and recent studies highlighting what is currently known about the relationship between genetic variation, biomolecular function, and disease.

GLI2 promotes cell proliferation and migration through transcriptional activation of ARHGEF16 in human glioma cells

BACKGROUND

The Hedgehog (Hh) signaling pathway plays critical roles in modulating embryogenesis and maintaining tissue homeostasis, with glioma-associated oncogene (GLI) transcription factors being the main mediators. Aberrant activation of this pathway is associated with various human malignancies including glioblastoma, although the mechanistic details are not well understood.

METHODS

We performed a microarray analysis of genes that are differentially expressed in glioblastoma U87 cells overexpressing GLI2A, the active form of GLI2, relative to the control cells. Chromatin immunoprecipitation and dual-luciferase assays were used to determine whether Rho guanine nucleotide exchange factor 16 (ARHGEF16) is a downstream target of GLI2. Then, transwell migration, EdU and soft-agar colony formation assays were employed to test effects of ARHGEF16 on glioma cancer cell migration and proliferation, and the effects of GLI2/ARHGEF16 signaling on tumor growth were examined in vivo. Finally, we performed yeast two-hybrid assay, Co-IP and GST-pull down to identify factors that mediate effects of ARHGEF16.

RESULTS

We found that ARHGEF16 mRNA level was upregulated in U87 cells overexpressing GLI2A relative to control cells. GLI2 binds to the ARHGEF16 promoter and activates gene transcription. Glioma cells U87 and U118 overexpressing ARHGEF16 showed enhanced migration and proliferation relative to the control cells, while knockdown of ARHGEF16 in H4 cells led to decreased cell proliferation compared to the control H4 cells. In contrast to the promoting effect of GLI2A overexpression on glioma xenograft growth, both GLI2 inhibition and ARHGEF16 knockdown retarded tumor growth. Cytoskeleton-associated protein 5 (CKAP5) was identified as an interaction protein of ARHGEF16, which is important for the stimulatory effects of ARHGEF16 on glioma cell migration and proliferation.

CONCLUSIONS

These results suggest that therapeutic strategies targeting the GLI2/ARHGEF16/CKAP5 signaling axis could inhibit glioma progression and recurrence.

Ovarian Tumor Microenvironment Signaling: Convergence on the Rac1 GTPase

The tumor microenvironment for epithelial ovarian cancer is complex and rich in bioactive molecules that modulate cell-cell interactions and stimulate numerous signal transduction cascades. These signals ultimately modulate all aspects of tumor behavior including progression, metastasis and therapeutic response. Many of the signaling pathways converge on the small GTPase Ras-related C3 botulinum toxin substrate (Rac)1. In addition to regulating actin cytoskeleton remodeling necessary for tumor cell adhesion, migration and invasion, Rac1 through its downstream effectors, regulates cancer cell survival, tumor angiogenesis, phenotypic plasticity, quiescence, and resistance to therapeutics. In this review we discuss evidence for Rac1 activation within the ovarian tumor microenvironment, mechanisms of Rac1 dysregulation as they apply to ovarian cancer, and the potential benefits of targeting aberrant Rac1 activity in this disease. The potential for Rac1 contribution to extraperitoneal dissemination of ovarian cancer is addressed.

MicroRNA-340 inhibits squamous cell carcinoma cell proliferation, migration and invasion by downregulating RhoA

BACKGROUND

MicroRNAs are reported to play an important role in tumor growth and metastasis, including squamous cell carcinoma (SCC). Accumulative evidence has revealed that dysregulated miR-340 expression contributed to the carcinogenesis and development of various cancers.

OBJECTIVE

The aim of the current study was to investigate the role and the underlying mechanism of miR-340 in SCC cell proliferation, migration and invasion.

METHODS

Quantitative real-time PCR was performed to examine the expression of miR-340 in SCC tissues and cell lines. The function of miR-340 in SCC was investigated through Cell Counting Kit-8, wound healing, transwell migration and invasion assays. Bioinformatics analysis, luciferase reporter assay, western blotting and immunohistochemical analysis were conducted to predict and confirm the target gene of miR-340.

RESULTS

In the present study, we first found that miR-340 was significantly decreased in both SCC tissues and cell lines. Moreover, ectopic expression of miR-340 remarkably attenuated SCC cell proliferation, migration and invasion, whereas inhibition of endogenous miR-340 promoted SCC cell proliferation, migration and invasion in vitro. Our subsequent bioinformatics analysis and luciferase reporter assay showed that RhoA was a novel direct target of miR-340 in SCC cells, and the knockdown of RhoA expression rescued the effects of miR-340 inhibition on SCC cell proliferation, migration and invasion. More importantly, the expression of RhoA and miR-340 was negatively correlated in SCC tissues.

CONCLUSION

Our findings demonstrate the tumor suppressor role of miR-340 in SCC by directly regulating RhoA. Therefore, restoration of miR-340 expression can be a potential therapeutic approach for SCC treatment.

The role of Rac in tumor susceptibility and disease progression: from biochemistry to the clinic

The family of Rho GTPases are involved in the dynamic control of cytoskeleton reorganization and other fundamental cellular functions, including growth, motility, and survival. Rac1, one of the best characterized Rho GTPases, is an established effector of receptors and an important node in signaling networks crucial for tumorigenesis and metastasis. Rac1 hyperactivation is common in human cancer and could be the consequence of overexpression, abnormal upstream inputs, deregulated degradation, and/or anomalous intracellular localization. More recently, cancer-associated gain-of-function mutations in Rac1 have been identified which contribute to tumor phenotypes and confer resistance to targeted therapies. Deregulated expression/activity of Rac guanine nucleotide exchange factors responsible for Rac activation has been largely associated with a metastatic phenotype and drug resistance. Translating our extensive knowledge in Rac pathway biochemistry into a clinical setting still remains a major challenge; nonetheless, remarkable opportunities for cancer therapeutics arise from promising lead compounds targeting Rac and its effectors.